1. Field of the Invention
The present invention relates to an electro-magnetic wave shielding structure which is provided for communication apparatus used for both transmitting and receiving, or for only receiving in ultra-short wave ranges and others, for example, a car-telephone. The invention relates particularly to such a shielding structure, which is arranged so as to sufficiently prevent disturbing interferences from itself and other devices, such that non-desired communication waves are not intermixed or emitted.
2. Related Art Statement
Generally, in the communication apparatus of this kind used, for instance, in ultra-short wave range, external waves, other than a desired wave, cause receiving obstructions by stray-coupling with receiver circuits, while a local oscillator output, leaking from a receiver circuit, disturbs other receivers. Thus, communication disturbances are frequently caused upon both to a particular communication apparatus and other communication apparatuses by undesired external waves other than desired waves transmitted and received through antennas, which intermix in the receiver circuit, or, by obstructive waves having undesired frequencies and emitted from the receiver circuit.
For preventing such communication disturbances, disturbance preventing means for entirely shielding cases of the apparatuses has been conventionally employed, such that essential portions of transmitter and receiver circuits are shielded through conductor materials suitable for cutting off leakage and stray coupling. Surfaces of insulating material cases made of plastics and the like for accommodating the communication apparatuses are applied with conductivity, and further electric power source connecting cables are wrapped with a metal net sheath covered by gummous material.
However, the shape and the size of shielding conductive materials applied on semi-conductor substrates provided for the communication apparatus circuit closely resemble wave lengths of disturbing waves. As a result, those conductive materials are operated as antennas for the disturbing waves. So that, particularly the leakage of the local oscillator output cannot be sufficiently suppressed by these means and hence frequently disturbs other receivers. Consequently, the sufficient shielding of non-desired waves has been a conventional problem. PG,4